For a battery case enclosing a strong alkaline liquid for an alkaline manganese battery, a nickel-cadmium battery and the like, a method such that a cold-rolled steel strip is press-formed into a battery case and then subjected to barrel plating or a method such that a nickel plated steel strip is press-formed into a battery case have conventionally been employed.
In this way, for the use of battery, such as an alkaline manganese battery, a nickel cadmium battery and the like, nickel plating is used because nickel is strong for alkaline corrosiveness and these batteries mainly utilize strong alkali potassium hydroxide as electrolyte. Further, in the case battery is connected to an external terminal, nickel has stable contact resistance. Furthermore, there is an advantage in the manufacture of battery that nickel has excellent spot weldability, in which spot welding is carried out to weld each constituent parts to be assembled in a battery.
In order to increase battery capacity in recent years, a DI (drawing and ironing) forming method is used instead of a deep-drawing method (JP-B-7-99686) as a press-formed method for a battery case. In the DI-forming method and a DTR (drawing thin and redraw) method, anode and cathode active substances can be enclosed in a larger amount corresponding to a smaller thickness of the side wall of the case than the thickness of the bottom, and an advantage can also be obtained such that the pressure strength of the battery can be improved owing to the thick bottom of the case along with an increase of battery capacity.
Furthermore, the demand of an alkaline manganese battery and a nickel hydoride battery has increased in recent years, and automization of production of batteries is progressing accordingly. Owing thereto, a battery case having been press-formed is automatically conveyed to a battery case washing machine and a battery producing machine with a belt conveyor. However, in the case where the outer surface of the battery has poor slipping property, the battery case is stopped on the way in on the belt conveyor to delay supply of the battery case to the battery washing machine or the battery production process, whereby the working efficiency is deteriorated.
In recent years, with respect to battery cases produced by the deep-drawing method, the DI-forming method and the DTR-forming method, a large amount of the battery cases are placed on a belt conveyor and run by for producing batteries. However, they do not run smoothly with a conventional nickel plating on the outermost layer of the outer surface of the battery case, whereby the supply of the battery cases is liable to be intermittent. In particular, upon entering the battery cases running on the belt conveyor into a process step of arranging them into lines, clogging is liable to occur with the nickel on the outermost layer of the outer surface of the battery case.
A technical object of the invention is to provide a battery case that is excellent in glossiness and runnability, and a surface-treated steel plate that can be preferably used for producing the battery case.